Xcode pauses inside JavaScriptCore when using the Chrome debugger

I’m experimenting with realm and react native. I have the following RN code:

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View
} from 'react-native';


var Realm = require('realm');

// Define your models and their properties
class Car {}
Car.schema = {
	name: 'Car',
	properties: {
		make:  'string',
		model: 'string',
		miles: 'int',
	}
};
class Person {}
Person.schema = {
	name: 'Person',
	properties: {
		name:    {type: 'string'},
		cars:    {type: 'list', objectType: 'Car'},
		picture: {type: 'data', optional: true}, // optional property
        birthday: {type: 'date'}
	}
};


Realm.Sync.User.login('http://localhost:9080', 'dd', 'xxxx', (error, user) => { console.log(error, user) });

export default class realmDBtest extends Component {

	constructor(props) {
		super(props);

		let user = Realm.Sync.User.current;

		this.realm = new Realm({
            schema: [Car, Person],
			sync: {
				user: user,
				url: 'realm://localhost:9080/~/cars',
			},
		});

		this.realm.addListener('change', () => {
			this.forceUpdate()
		});
	}

  render() {
	  let cars = this.realm.objects('Car').filtered('miles > 1000');


	  var carsOutput = cars.map(el => {
	    return (
	        <View>
              <Text>{el.make} - {el.model} - {el.miles}</Text>
            </View>
        )
      });

	  return (
      <View style={styles.container}>
          {carsOutput}
          <Text onPress={() => {
			  this.realm.write(() => {
                  let myCar = this.realm.create('Car', {
                      make: 'Honda',
                      model: 'Civic',
                      miles: 2000,
                  });
                  myCar.miles += 20; // Update a property value
              });
            }
          }>Add car </Text>

        <Text onPress={() => {
			console.log(this.realm.syncSession);
			}}>log session</Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

AppRegistry.registerComponent('realmDBtest', () => realmDBtest);

When I use the app for no apparent reason the app stalls and xcode is showing the following:

JavaScriptCore`JSC::Heap::releaseAccessSlow:
    0x108b62110 <+0>:   pushq  %rbp
    0x108b62111 <+1>:   movq   %rsp, %rbp
    0x108b62114 <+4>:   pushq  %r14
    0x108b62116 <+6>:   pushq  %rbx
    0x108b62117 <+7>:   movq   %rdi, %r14
    0x108b6211a <+10>:  movl   0x488(%r14), %eax
    0x108b62121 <+17>:  testb  $0x4, %al
    0x108b62123 <+19>:  je     0x108b62182               ; <+114>
    0x108b62125 <+21>:  leaq   0x488(%r14), %rbx
    0x108b6212c <+28>:  nopl   (%rax)
    0x108b62130 <+32>:  testb  $0x2, %al
    0x108b62132 <+34>:  jne    0x108b62194               ; <+132>
    0x108b62134 <+36>:  movl   %eax, %ecx
    0x108b62136 <+38>:  testb  $0x10, %al
    0x108b62138 <+40>:  jne    0x108b62150               ; <+64>
    0x108b6213a <+42>:  testb  $0x1, %al
    0x108b6213c <+44>:  jne    0x108b62170               ; <+96>
    0x108b6213e <+46>:  andl   $-0x5, %ecx
    0x108b62141 <+49>:  lock   
    0x108b62142 <+50>:  cmpxchgl %ecx, (%rbx)
    0x108b62145 <+53>:  jne    0x108b6217c               ; <+108>
    0x108b62147 <+55>:  jmp    0x108b62183               ; <+115>
    0x108b62149 <+57>:  nopl   (%rax)
    0x108b62150 <+64>:  andl   $-0x11, %ecx
    0x108b62153 <+67>:  lock   
    0x108b62154 <+68>:  cmpxchgl %ecx, (%rbx)
    0x108b62157 <+71>:  jne    0x108b6217c               ; <+108>
    0x108b62159 <+73>:  movq   %r14, %rdi
    0x108b6215c <+76>:  callq  0x108b621a0               ; JSC::Heap::finalize()
    0x108b62161 <+81>:  movq   %rbx, %rdi
    0x108b62164 <+84>:  callq  0x108fa08a0               ; WTF::ParkingLot::unparkAll(void const*)
    0x108b62169 <+89>:  jmp    0x108b6217c               ; <+108>
    0x108b6216b <+91>:  nopl   (%rax,%rax)
    0x108b62170 <+96>:  andl   $-0x7, %ecx
    0x108b62173 <+99>:  orl    $0x2, %ecx
    0x108b62176 <+102>: lock   
    0x108b62177 <+103>: cmpxchgl %ecx, (%rbx)
    0x108b6217a <+106>: je     0x108b62188               ; <+120>
    0x108b6217c <+108>: movl   (%rbx), %eax
    0x108b6217e <+110>: testb  $0x4, %al
    0x108b62180 <+112>: jne    0x108b62130               ; <+32>
    0x108b62182 <+114>: int3   
->  **0x108b62183 <+115>: popq   %rbx**
    0x108b62184 <+116>: popq   %r14
    0x108b62186 <+118>: popq   %rbp
    0x108b62187 <+119>: retq   
    0x108b62188 <+120>: movq   %rbx, %rdi
    0x108b6218b <+123>: popq   %rbx
    0x108b6218c <+124>: popq   %r14
    0x108b6218e <+126>: popq   %rbp
    0x108b6218f <+127>: jmp    0x108fa08a0               ; WTF::ParkingLot::unparkAll(void const*)
    0x108b62194 <+132>: int3   
    0x108b62195 <+133>: nopw   %cs:(%rax,%rax)

I can continue with the program execution and the app doesn’t crash, but it’s extremely annoying and I wonder what all this means and would it affect an app in production?

Also what I noticed is that my app doesn’t update when I do an update on the remote Database. Basically my change event is not triggered, but if I relaunch the app - I have the correct data.

[jeremyong]

I’m seeing this as well. Makes debugging a realm-enabled app very difficult

[esutton]

@scottwio Sadly, I had to largely abandon Chrome debugging.

When developing new features for my app, I must add (and then remember to remove) many console.log statements, then use adb logcat or xcode to develop and debug. It is a significant hit on efficient development.

A single package ( realm ) prevents efficient Chrome debugging of anything.